From: Tatsuo Ishii <ishii@sraoss.co.jp>
Date: Fri, 21 Jun 2024 05:21:15 +0000 (+0900)
Subject: Fix MAIN_NODE macro (actually pool_virtual_main_db_node_id()).
X-Git-Tag: V4_4_8~16
X-Git-Url: http://git.postgresql.org/gitweb/static/gitweb.js?a=commitdiff_plain;h=152c65d6f142a92b70b3c04a21a701baa6a36e21;p=pgpool2.git

Fix MAIN_NODE macro (actually pool_virtual_main_db_node_id()).

The macro used to REAL_MAIN_NODE_ID if there's no session context.
This is wrong since REAL_MAIN_NODE_ID can be changed any time when
failover/failback happens.  Suppose REAL_MAIN_NODE_ID ==
my_main_node_id == 1. Then due to failback, REAL_MAIN_NODE_ID is
changed to 0. Then MAIN_CONNECTION(cp) will return NULL and any
reference to it will cause segmentation fault. To prevent the issue we
should return my_main_node_id instead.

Discussion: https://www.pgpool.net/pipermail/pgpool-general/2024-June/009205.html
Backpatch-through: V4.1
---

diff --git a/src/context/pool_query_context.c b/src/context/pool_query_context.c
index 230a116b7..1ba02c712 100644
--- a/src/context/pool_query_context.c
+++ b/src/context/pool_query_context.c
@@ -361,7 +361,16 @@ pool_virtual_main_db_node_id(void)
 	sc = pool_get_session_context(true);
 	if (!sc)
 	{
-		return REAL_MAIN_NODE_ID;
+		/*
+		 * We used to return REAL_MAIN_NODE_ID here.  Problem with it is, it
+		 * is possible that REAL_MAIN_NODE_ID could be changed
+		 * anytime. Suppose REAL_MAIN_NODE_ID == my_main_node_id == 1. Then
+		 * due to failback, REAL_MAIN_NODE_ID is changed to 0. Then
+		 * MAIN_CONNECTION(cp) will return NULL and any reference to it will
+		 * cause segmentation fault. To prevent the issue we should return
+		 * my_main_node_id instead.
+		 */
+		return my_main_node_id;
 	}
 
 	if (sc->in_progress && sc->query_context)